1. Field of the Invention
The invention pertains generally to acoustic wave communication. More particularly, the invention relates to sonar systems. In greater particularity, the invention pertains to acoustic image conversion as it relates to time varying gain sonar.
2. Description of the Related Art
Submarines navigating underice have relied on monochromatic sonar systems to provide them with a visualization of objects to be avoided. Traditional systems have included phosphor cathode ray tubes that are sensitive to ambient light variations, making range, bearing and elevation information, regarding ice ridges and the like, vulnerable to being obscured or otherwise less readable. Many of these sonar setups rely upon increasing shades of brightness to indicate respectively higher degrees of hazard associated with approaching an underwater ridge or peak.
These levels of brightness often indicate the clearance that exists between the top of the vessel and the lowest extent of the approached ice ridge. Navigators determine whether this clearance is increasing or decreasing by observing changes in the brightness levels. With sonar systems of this kind, the navigator-operator must visually discern and commit to memory these changes as his vessel advances.
Monitoring these often subtle changes strains the operator and can increase his fatigue and possibility of poor judgement. In addition, if the ambient light level in the sonar console compartment is changed, such as due to changing operational conditions, for example, then the relative magnitudes of displayed brightness have an apparent change to the operator's eyes, so that a truly hazardous obstacle may not be recognized as such. The effects of fatigue and strain on the operator are sped up, and the risk of disastrous collision is increased.
Thus there is a continuing need in the state of the art for a sonar display that provides an operator with a portrayal of underwater obstacles that is easy to understand, not sensitive to ambient lighting and that can convey meaningful information for responsive action.